1. Field of the Invention
The present invention relates to an electric power steering system and a method of outputting a steering angle thereof.
2. Description of the Prior Art
As a means for ensuring the stability of a steering state by reducing steering force of a steering wheel, a power steering system may be applied to a vehicle. Such a power steering system may be classified into a Hydraulic Power Steering (HPS) system using hydraulic force and an Electric Power Steering (EPS) system using rotational force of a motor.
The electric power steering system includes an Electronic Control Unit (ECU) configured to control the driving of a motor according to a running state of the vehicle sensed by, for example, a torque sensor that senses the torque of a steering shaft and a vehicle speed sensor that senses the speed of the vehicle in such a manner that while moving at low speeds, light and convenient steering feeling may be provided, while moving at high speeds, a heavy and good direction stability may be provided, and in an emergency situation, rapid steering may be performed. As a result, the electric power steering system may provide optimum steering conditions to a driver.
In the electric power steering system, the torque sensor may include a device configured to measure an absolute steering angle and a device configured to measure a relative steering angle. The ECU may calculate the final desired absolute steering angle using the measured absolute steering angle and relative steering angle.
In order to ensure the reliability of the measured final absolute steering angle, verification of the absolute steering angle and the relative steering angle measured by the devices is required. In particular, according to the introduction of ISO 26262 (“Road vehicles—Functional safety”) standard absolute, high reliability for the steering angle is demanded.